Instrument field testing set



INSTRUMENT FIELD TESTING SET Filed April 5, 1940 5 sheetshsmaet 1 .118k I a la Lg) JQL l Dl /N VEN To!! Feb. 16, 1943. H. N. LUMM INSTRUMENT FIELD TESTING SET Eiled April 5, 1940 5 Sheets-Sheet 2 MMU /Nve/vraq WE1/EV /V. L MM 4 @Az/Veys Feb. 16, 1943. H, LUMM INSTRUMENT FIELD TESTING SET Filed April 5, 1940 5 Sheets-Sheet 3 I un LEE @Numb 0% m H. N. LUMM INSTRUMENT FIELD TESTING SET Feb. 16, 1943.

Filed April 5, 1940' m 114110111111 a v mi-A@ 5 Sheets-Sheet 4 '//v VEN me Feb. 16, 1943. H, N LUMM 2,310,974

INSTRUMENT FIELD TESTING` SET Filed April 5, 1940 5 Sheets-Sheet 5 o o/o o-o/o o olo o Q76 L/75 L16/ /jv VEN rox? HARVEY /V. UM/V Patented Feb. 16, 1943 UNITED STATES PATENT OFFICE 2,310,974 INS'FRUltiENT FIELD TESTING SETI Harvey Newton Lumm, Dayton, Ohio Application April 5, 1940, Serial No. 328,055

9 Claims. (Cl. 'I3-51) (Granted under the'act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to testing apparatus and more particularly relates to a portable instrument field testing set for making tests on various aircraft instruments without removing the instruments from the airplane. y

Portable devices for testing aircraft instruments have been used in the art and a resum of the known practice of the prior art is contained in an article entitled A course for ground engineers, part 1X, by R. W. Sloley in the British publication, Aircraft Engineering, for April 1930, pages 92 to 97, inclusive, and some of the methods of testing there disclosed, are employed in the present invention. However, so far as I am aware, the testing devices employed in the prior art have had no relation to each other,

, while according to the invention routine check tests on instruments of the type employing positive pressures and on other instruments employing negative pressures, may be readily accomspeed control means operable for either the fluid pressure tests, -or for tachometer testing.

Other objects and novel features of the invention will be pointed out or become apparent by reference to the construction, combination. and arrangement of parts hereinafter fully described and villustrated in the drawings in which:

Fig. 1 illustrates a side elevation of the portable testing unit with the principal elements thereof mounted on a wheeled carriage or dolly, and;

Fig. 2 illustrates a view of a controly valve assembly taken on line 2-2 of Fig. l, and;

Fig. 3 illustrates a view of the clutch 'and tachometer drive means taken on line 3-3 of Fig. l, and;

Fig. 4 is a sectional view taken on line 4--4v tube serving as a suction source for gyro instruments, and:

Fig. 'l illustrates la novel means for attaching a test hose to the Pitot tube of a Pitot-static head, and;

Fig, 8 illustrates a novel means for attaching a test hose to the static tube oi a Pitot-static head.

Fig. 9 illustrates an altimeter testing chamber for use with the system illustrated in Fig. 5, and;

Fig. l0 illustrates a modication of thealtimeter testing device voiz Fig. 6, arranged for testing rate of climb indicators as well as altimeters.

cable 5, may be connected to any suitable current supply source such as an outlet box lin an airplane hanger, or t-o the generator of a portable gasoline engine driven power supply (not shown). The motor 6, may be of either the alternating current, or direct current type, or may be of dual construction including an alternating `current motor and a direct current motor contained Within the same motor frame, but of course only one of the motors being in use at a time, such a lconstruction is essential where for example only alternating current is available in the aircraft hangers, while the portable engine driven generator develops direct current. The motor 6, is provided with a power output shaft 'l and amanually actuated speed control unit 8, which in the dual type motor consists of two units, a brush shifting device in the alternating current motor and a speed control yrheostat for the direct current motor unit, the two controls being separate and distinct. The motor shaft 1, is connected by a flexible couplings, to a plural drive clutch unit generally indicated by the reference numeral I0, which by means of a manual control 21, may drive either the tachometer drive unit I8, or the pump 35. The pump 35, has an inlet conduit 36 and an outlet conduit 31, each of which are connected to a four way control valve 38, which also connects to an air inlet, or discharge conduit 40 and a conduit 4I which is connected to a rotary plug valve 42, which in turn is connected by a conduit 45 with an air reservoir 46. The reservoir 46 is provided with an outlet conduit 50, having a filter 49, inserted therein. The conduit 50, is connected in an instrument test system hereinafter more fully described.

'Ihe various master test instruments, valve and speed control means, etc., are mounted on an instrument board |00, supported on the main frame of the dolly I.

Fig. 2 illustrates the arrangement of the control valve 39 and a control valve 51, in the device of Fig. 1, for simultaneous manual actuation. A valve rod 62, rotatably connecting the rotatable valve plugs 39 and 58 of the respective valves 38 and 51, is actuated by a control knob 63, on the instrument panel I00.

Figs. 3 and 4 illustrate the clutch mechanism I0, of Fig. 1, for driving the pump 35, or the tachometer drive I8. The flexible coupling 9, driven by the motor shaft 1, connects to a clutch driving shaft II, which has an annular sleeve I2, slidably keyed thereon and the sleeve isprovided at one end with teeth I3, which mesh with corresponding teeth I4, on the face of a spiral tooth gear I5, loosely rotatably mounted concentric with shaft II. The gear I5, meshes with a gear I6, which rotates in a plane perpendicular to the plane of gear I5 and drives a shaft I1, which serves as a drive shaft for the tachometer drive I8. .The tachometer drive I8, has two tachometer drive take-offs I9 and 20, arranged at right angles and respectively adapted to drive a test tachometer cable 2| and a master tachometer cable 23 (Fig. 5). By shifting the sleeve I2. axially to the right as seen in Fig. 4, the teeth I3 and I4 will be de-meshed and the tachometer drive will be disconnected from motor 6 and continued shifting of the sleeve I2, to the right, will cause the teeth 30, on the right end of the sleeve I2, to mesh with corresponding teeth 3|, on the face of a driving flange 32, adapted to drive the pump 35. The sleeve I2, is provided with a central annular groove 25, for receiving an` eccentric disc 26, located on the end of a shaft element 21, mounted in the clutch casing I0, in a plane at right angles to the axis oi' the shaft II and sleeve I2. The shaft element 21, is adapted to be rotated by a rod 28, secured to the knob 29 (Fig. 1), rotation of the shaft 21 and its eccentric portion 26, shifting the sleeve I2, to either drive the tachometer take-olf I8, or the pump 35.

Referring now to Fig. 5, in which the general arrangement of the elements of the test set is schematically shown: The clutch I0, may drive the shaft I1 and tachometer drive I8, as previously noted and the tachometer .take-off connection I 9, drives. a test tachometer cable 2I, which may be connected to drive a tachometer 22, mounted on the instrument board of the air- Diane and the calibration of which it is desired to check. The tachometer take-01T 20, connects to a tachometer cable 23, which drives a master tachometer 24, mounted on the instrumentpanel |00, of the portable testing set.

As above noted the clutch T0, may be engaged to drive the air pump 35, which may be of any suitable type, such as a vane pump or a diaphragm pump. Where a vane, `or other pump of the type requiring lubrication is employed, oil may be injected into the inlet side of the pump and separated out of the air discharged from the pump, by an oil separating means not shown in the drawings. Where a diaphragm type of pump is employed, no oil will come in reservoir, or vacuum tank 46.

. indicator 10.

contact with the air being pumped, and a sepa.- rator will not be required. The inlet conduit 36 and the outlet conduit 31, of the pump 35, are each connected to the plug valve 38, which is also connected to an inlet-discharge pipe 49 and to a conduit 4I, which in turn is connected to the rotary plug valve 42, conduit 45 and the air The valve plug 39, of the valve 38, is provided with ,two valve passages and in the position shown in Fig. 5, the conduit 40, is connected to the inlet conduit 36, of the pump 35 and the pump receives air from the outside atmosphere through the conduits 40 and 36. The air discharged from pump outlet conduit 31, is conducted by the other passage in the valve plug 39, to the conduit 4I and with the valve plug 43, in the position shown in Fig. 5, the air will pass to conduit 45 and reservoir tank 46 and will build up a pressure determined by a pressure relief valve 41, connected to the tank 46. Air under pressure from tank 46, passes through an outlet line 50, havl ing a filter 49, incorporated therein. The outlet line 50, is connected to a vacuum or -pressure l control valve 5I, the needle valve of which is actuated by a. control knob 52, on the instrument panel I00 (Fig. l). The valve 5I, is connected to a conduit 53, which connects to a gage control valve 51 and the conduit 53, also connects to a branch conduit 54, which terminates in a hose connection fitting 55, to which a flexible test hose 56, of any suitable length may be connected. The test hose 56, may be connected to any one of the various instruments which are to be tested and indicated in Fig. 5, by reference numerals 19 to 8|, inclusive. The gage valve 51, is connected to a conduit 66 which is connected to the pressure connection P, of a master air speed indicator 19. The conduit 66. is also connected in parallel to a branch conduit 61, which connects to the pressure side P, of a master vacuum-pressure gage 68. The valve 51, is also connected to a conduit 64, which is connected to the suction connection S, of the master air speed indicator 10 and also connectedV in parallel with the branch conduit 65, which is connected to the suction side S, of the master vacuum-pressure gage 68. The gage control valve 51, is provided with a rotary valve plug 59, which has a passage 6I, formed therein, and in the position shown in Fig. 5, connects conduit 53, with the conduit 66 and the pressure sides of the master gage 68 and the master air speed Rotation of the valve plug 58, through ninety degrees in a counterclockwise direction will cause passage 6I, in the valve plug 58, to connect the conduit 53, to the conduit 64 and the suction sides of the master gage 68 and the master air speed indicator 19. The valve plug 58, is provided with a groove 59, which always remains in communication with the vent opening 6I), formed in the valve casting. With the valve plug 58, in the position shown in Fig. 5, the groove 59, vents the conduit 64 and the suction sides of the master gage 68 and the master air speed indicator 10, to the atmosphere through the vent opening 60. When the valve plug 58, is rotated so as to connect the conduits 53 and 64, the conduit 66 and the pressure sides of the master gage 68 and the master air speed indicator 18, will be vented to atmosphere through the groove 59, of valve plug 58 and vent opening 68.

With the parts as shown in Fig. 5 air under pressure from tank 46, will appear in conduit 58,

when valve is opened and air under pressure will flow into the conduit 54 and test hose 53 and to the instrument connected thereto. Air under pressure will also flow from conduit 53, through valve 51, to conduit 66 and to master vacuum-- pressure gage 58, and master air speed indicator 10, on the pressure sides thereof, thus permitting the readings thereof to be compared with the instrument being tested.

If now it is'desired to make an instrument test, in which a vacuum of low value is required, the valve plug 39, of the valve 38, is rotated counterclockwise from the position shown in Fig. 5,

through an angle of ninety degrees by actuation y of the knob 63 (Figs. 1 and 2) and valveplug 58, of valve 51, will also be rotated an equal amount in the same direction. The pump inlet conduit 36, will now be connected to the tank 48, through conduit 45, valve 42 and conduit 4|, so that the pump 35, will create a vacuum in tank 45, limited by the vacuum relief valve'48. A vacuum will then exist in conduits 50, 53 and 54 and in test hose 55. The valve plug 58, of valve 5.1, is now in the position to connect conduit 64 and the suction sides of the master vacuum-pressure gage 68 and master air speed indicator 10, to the conduit 53 and to the vacuum condition existing therein, the positive pressure gage line 66, being vented lto the atmosphere in the manner above described.

Air withdrawn from the systemthrough inlet conduit 36, is discharged from the discharge side of the pump 35, through conduit 31, valve plug 39 and the conduit 40, to the atmosphere.

In view of the above disclosure it is evident that a fluid pressure either above or below atmospheric pressure, may be created in the test hose 56 and the value of this pressure. either in terms of absolute pressure, or in terms of velocity in miles per hour, as indicated respectively by the master vacuum-pressure gage 58 and the master` air speed indicator 10, may be measured. The total range of the vacuum-pressure gage 58, is about inches of mercury, or roughly 5 lbs. per square inch absolute, which range has been found satisfactory for -all necessary routine check tests.

During a test any desired pressure, or vacuumy within the instrument range may be maintained by actuation of the control valve 5I which can be completely closed upon the desired pressure. or vacuum `condition being attained the pressure relief valve 41, or vacuum relief valve 48,-preventing an overloading of the continuously running pump` 35 and motor 6. The proper pump speed may be adjusted by actuation of the speed control 8, of motor 6, by the control knob 8' on the instrument panel I 00 (Fig. 1).

For testing air turbine driven gyroscopes invarious instruments such as pitchand turn indicaand to provide such a vacuum, the valve 42, is employed. As seen in Fig. 5, the valve 42. is connected to a conduit--1I,provided with aterminal connection 12, to which a flexible test hose 14.

maybe connected. The valve 42, is provided with rotatable valve plug 43, formed with a T shaped passage and when 'the valve plug 43, is rotated ninety degrees in'a. clockwise direction from the the speed of the pump and by means of the relief .nstruments valve provided in the airplane on the vacuum line leading to the4 instruments. `The vacuum gage provided on the instrument, or separately mounted on the aircraft instrument panel gives the -indication of the suction pressure applied to the By leaving the valve 38, in the pressure position as shown in Fig. 5 and rotating the valve plug 43, to the position above described, a positive pressure of a higher magnitude could be developed in the test hose 14, if for any reason such a pressure were required for testing purposes.

By means of the above described fluid pressure system, it is seen that we may develop a predetermined pressure, or vacuum, Within a desired test range in the test hose line 56 and we may also develop a high vacuum in the test line 14, for testing instruments requiring a high vacuum, by manipulating the control valves provided.

OPERATION Tachometer testing In order to test the engine tachometer, or tachometers, on an aircraft with the portable eld test set, the extension flexible test cable 2l, is connected to drive the tachometer to be tested indicated by numeral 22, by connecting the test' cable to the tachometer drive cable at the engine driving connection, or in the case of an electrical tachometer by disconnecting the generator unit tors, a comparatively large vacuum is necessary Y from the engine drive and connecting the generator to the test tachometer cable 2l.' The clutch control knob 29, on the control panel |08 (Fig. 1) is .then actuated, to cause clutch II), to connect motor 6, to drive tachometer drive I8, in the manner previously described. The motor 6, is then energized by actuation of a suitable switch, controlled by knob M (Fig. 1), the motor 'be checked by varying the motor speed in the manner above described. y

Pressure tests In order to'accompllsh pressure tests on instruments such as a fuel pressure gage-manifold pressure gage, or air speed indicator (Pitot tube side) as indicated in Fig. 5 by the legend Pressure tests, the test hose 58, is connected to the pressure line of the instrument to be tested and the valve control knob 83 (Fig. 1), is actuated so as to place the valves 38 and 51, in the position for a pressure test and the knob 44 (Fig. 1) actuated to position the valve 42, in the position shown in Fig. 5. The pump 35, is connected to motor 6, by manual lactuation of the clutch I8, by control knob 29 '(Fig. 1), in the manner previously described. The control valve 5|, is closed by actuation of the knob 52 (Fig. -1) and the motor 5, is energized and adjusted to a suitable speed by motor speed control 8. 'I'he valve 5I, is then slowly opened and? the pressure,

and/or air speed indicated by the instrument to' be tested is 'checked against the pressure reading of the master vacuum-pressure gage 68, or the air speed vindicator 10. By closing valve 5I, after a predetermined pressure is reached, in-

strument casing or line leaks may be detected by noting whether the instrument maintains the reading for a certain period of time. If leaks are detected, the test hose may be connected directly to the instrument being tested, to determine if the leak is in the instrument casing, if this test is satisfactory then the leak in the line must be traced.

Vacuum tests on instruments other than air driven gyra-instruments Instruments requiring a test pressure below atmospheric pressure, or a vacuum, arev vacuum gages, manifold pressure gages, air speed indicator (static pressure side) and instruments such as rate of climb indicators connected to the static pressure line. Manifold pressure gages on modern high power engines must be tested for both positive and negative pressure due to the fact, that the manifold pressure may be negative and change to positive pressure upon using a moderate degree of supercharging, hence both pressure and vacuum tests are often required. Some of the instruments requiring vacuumy tests are indicated in Fig. by the numerals 88 to 8l, inclusive. The test hose 56, is connected to the instrument lines, except that in making the connection for either pressure or vacuum test on the air speed indicator 88, a connectionis made to the Pitot static head in a manner hereinafter described.

The procedure for the vacuum test is exactly the same as for making a pressure test, as above described, except that the valve plug 39, of the valve 38, is positioned by knob 63 (Fig. 1), to connect the pump inlet conduit 36, to the conduit 4I, to produce a vacuum in test hose 56 and valve plug 58, is positioned by knob 63, to connect conduit 53, with conduit 64 and the suction sides of master vacuum-pressure gage 68 and master air speed indicator 18, in the manner previously described. Needle valve 5I, is initially closed and is gradually opened allowing a vacuum to gradually be produced in the test hose 56. The readings of the master gage 68 and the master the instruments is then adjusted by actuation of the relief valve on the airplane.

Fig. 6 illustrates the means for attaching the vacuum test line 14, of the portable test set I, to test air`-turbine gyro instruments employing a Venturi tube mounted on the exterior of the aircraft, as a. ysuction source. The Venturi tube 85, is connected to the instrument suction line 15 and in night air flowing at high velocity through the Venturi tube causes a high vacuum at the Venturi throat, which produces a vacuum in the instrument suction line and to produce an equivalent test suction in the instrument line 15, without disconnecting the line from the venturi, a novel Venturi sealing means is employed. The sealing means comprises a tubular member 88, having a branch connection 81, to which the test hose 14, may be attached. The inner end of the tubular member 86, is open and its outer end is closed by a plug 88, which also has formed therewith an extension rod 89, threaded at its outer end. A tapered annular rubber plug 9|, is mounted on the inner end of the tubular member 86 and is suitably secured in sealing relation thereto by vulcanizing or clamping. A sleeve member 9|, having a longitudinal threaded bore adapted to be screwed onto the threaded end of the rod 89, is provided with an enlarged lmob 92, at its outer end. A tapered annular rubber plug 93, is mounted, on the sleeve 9|, adjacent its inner end and bonded thereto. The sealing device is assembled by inserting the rod 89 and rubber plug'98, into the front of the Venturi tube, until the plug 98 engages the tapered wall of the Venturi tube, the sleeve member 9 I, is then inserted in the rear Venturi opening and threaded onto the end of rod 89, by turning knob 92, until the plug 93, comes into tight sealing Y engagement with the inner walls of the Venturi air speed indicator 18, are compared with the reading of the instrument in the airplane.

Procedure ,for testing gyra instruments As above noted in the description of Fig. 5, in order to test the air drivengyros employed in a number of instruments a rather high vacuum is required, so that for such tests, the test hose 14, is employed and if the source of vacuum employed for driving the gyros is an engine driven pump, the vacuum line 15 is disconnected at the pump and connected to the test hose line 14. If the instrument vacuum line 15, is connected to a Venturi tube mounted on the exterior of the aircraft, the test hose is connected by a novel ntting in a manner hereinafter described. The procedure for obtaining a vacuum in the test hose 14, has been above described with reference to Fig. 5, i. e., placing the valve plug 89, in the vacuum test position and rotating the valve plug 43, of valve 42, in a clockwise direction as seen in Fig. 5, by actuation of knob 44 (Fig. 1) thus placing conduit 4I, in communication withv test conduit 1I and test hose 14. Clutch |8is engaged to connect pump 35, to be driven by motor 6 and the motor speed is adjusted so that a. proper suction on the instrument, or instruments 16, is indicated on the vacuum gage 11, mounted on the airplane instrument panel, or incorpo rated in the instrument case. The suction on tube. 'Ihe Venturi tube is thus sealed from the outside atmosphere, while the throat of the venturi and suction line 15, are in free communication with the interior of tubular member 86 and connection 81. The test hose 14, may then be connected tothe connection 81 and the test may be performed in the mannerabove described. The use of the above fitting greatly facilitates testing, since it is not necessary to disconnect any parts of the instrument suction system in order to make the gyro test.

Fig. '1 illustrates the means for making the Pitot tube, or pressure test on the air speed indicator 88, with the portable test set, without it being necessary to break any connections in the airplane, the test hose 56, being connected by a novel fitting to the Pitot tube, of the Pitotstatic head, usually mounted on a bracket secured to the airplane wing. The Pitot static head is generally indicated by the reference numeral |85 and generally comprises an outer tubular member |86, provided with static pressure openings |81, communicating with the outside atmosphere and the tube |86, adapted to be connectedby a suitable conduit to the static pressure side S, of the airspeed indicator 98, the outer end of the static pressure tube |86 being closed by the annular head |88, which serves also to seal the tube |86, from the inner dynamic pressure, or Pltot tube I89,which is adapted to be connected to the pressure or Pitot side of the air speed indicator 88. The fitting for connecting the test hose 56, to the Pitot tube |89, comprises a thin tubular sleeve |I8, which is closed at one end by the head I I8, which terminates in a'conventional screwed connection ||4, to which the or tank 46.

2,310,974 hose line 56, may be attached. The head lll,y

compress the rubber sleeve IIB, tightly around the static pressure tube |06, thus sealing the Pitot tube |09, from the outside atmosphere. By connecting the test hose 56, to the connection ||4, the pressure test of the air speed indicator 80, may proceed in the manner above described.

Fig. 8 illustrates the means for connecting the test hose 56, to the static tube |06, of the static head |05, in order to carry out the vacuum, or static pressure tube test oi' the air speed indicator 80, or a rate of climb indicator, which as a rule also connects to the static pressure line. The connecting device comprises, a metal sleeve |20, which adjacent each end has an annular rubber sealing ring |24, the rings being spaced to leave a chamber or space |23, therebetween. A branch pipe |2|, having a screwed connection |22, at its lower end communicates with the space or chamber |23. The sleeve |20, is slotted at each end as at |25 and provided with screw clamping lugs |26, so that the sleeve I 20 and rubber sealing element |24, may be slipped over the static pressure tube |06, so that the static pressure openings |01, lie intermediate the sealing rings |24. By clamping the sealing rings |24, by means of screws (not shown) cooperating with the lugs |26, the chamber |23, is eiectively sealed from leakage along the static pressure tube and by connecting test hose 56, to the tube |2I, the vacuum test of air speed indicator 80, may proceed in the manner above described.

Fig. 9 illustrates the use of a vacuum test chamber in conjunction with the portable testing set, for testing the calibration of altimeters and such equipment will of course only be necessary where the portable test set is used at a place where instrument calibration equipment is not available. 'I-he altimeter testing equipment comprises a metal chamber |50, provided heavy glass observation window |5I. At one end the chamber is provided with a removable closure |52, which permits an altimeter |60 and a master altimeter |,6|, to be inserted into `'the chamber and seale'd'from the outside atmosphere by clamping on the closure |52. Atwits other end the chamber |50, is provided with a pipe connection |53, to which may be connected a conduit |54, having a control valve |55, inserted therein. The conduit |54, is connected to an outlet |56, of the tank 46, of the portable test set I, above described.

The altimeter |60, to be tested, is insertedin the chamber 50, along with the master altimeter |6I and the closure |52, clamped in place, the needle valve |55, and valve 5|, ofthe portable.

test set are then closed and the vacuum relief valve 48, on thereservoir 46,i is set, so that a high vacuum may -be produced in the reservoir,

The p'ump 35, is placed in operation with the control valves 38,42 and 51, placed in the vacuum test position. .The pump 35, will then evacuate reservoir, or tank 46 and test chamber |50 and by regulating valve |55, the

with al During the test the reading of altimeter |60, is

compared with the reading of master altimeter |6|. The action of the altimeter during a descent can be checked by opening valve |55.i thus venting the test chamber to the atmosphere.

It should also be noted that in place of connectl ing the test chamber |50, conduit |54 and valve |55,` to thereservoir or tank 46, they may instead be connected to the high vacuum gyro test con-r v nection 12.

Fig. 10 illustrates a modification of the altimeter testing device of Fig. 9, so that rate of climb f' indicators may be tested. The only cha-nge in .the system illustrated in Fig. 9, isthat a valve and leak assembly |10, is inserted in"'series with conduit |54, in place of the valve |55, of Fig. 9. The assembly |10, includes a capillary leak tube |12, controlled by a. needle valve |13, which may be adjusted to vary the rate of discharge trirough the capillary tube.

The test is carried out by inserting a master altimeter |6|, a master rate of climb indicator 15 and a rate ofy climb indicator |16, to be tested,

vin the test chamber |50. -The chamber |50, is

then evacuated in the manner described above with reference to Fig. 9 and upon a pressure equivalent to some desired altitude being attained, as indicated by the master altimeter |6|, the valve 42, (Fig. 5) is adjusted to block the conduit and the volume of ibothtank 46 and chamber |50, is available as a fluid pressure source. The needle valve |13, is then opened to obtain a desired rate of change of pressure within the test chamber, which will be indicated as a rate of climb on the master' rate of climb indicator |15 and the indication of the rate of climb indicator |16, is compared with the reading of the master instrument |15.

The portable test unit also incorporates a manually operated pump for testing oil pressure gages, against the reading of a master gage connected to the pump and a conventional thermometer testing unit is also provided, but neither of these units form a part of the invention claimed herein.

I have disclosed a portable testing unit for testing aircraft instruments, which is very compact andproven in service to greatly facilitate routine tests necessary in the proper maintenance of aircraft, due to thefact that a single test apparatus is adapted to make a plurality of different type of tests. The various tests are of course mainly for ications may be made coming within the scope of the invention as defined by the appended claims.

I claim:

1. In an instrument testing device of the character described a fluid conduit adapted to be connected to a vacuum or pressure responsive indicating instrument to be tested, a pump, a rst valve means connecting said pump and said uid conduit and operative in one position to cause said pump to create a uid pressure above atmospheric pressure within said conduit and operative -f v in a second position to evacuate said uid conduit vacuum in the test chamber may be varied.

to a pressure below atmospheric pressure, a master fluid pressure measurlngmeans including4 a positive pressure conduit and a negative pressure conduit, a second valve means for respectively connecting said positive pressure and said neganected at one end thereof to pressure or vacuumv tive pressure conduits to said fluid conduit and means for simultaneously actuating said ilrst and second valve means such that when said first valve means is in said one position said second valve means connects said positive pressure conduit to said iiuid conduit and when said first valve means is in said second position said second valve means connects said negative pressure conduit to said fluid conduit.

2. The structure as claimed in claim 1, in which said second valve means includes a vent communicating with the atmosphere and arranged such that when when said valve is in a position to connect one of said positive or negative pressure conduits to said uid conduit the other of said positive or negative pressure conduits will be vented to the atmosphere.

3. The structure as claimed inclaim 1, including an adjustable variable speed power means for driving said pump.

4. The structure as claimed in claim 1, including an air reservoir connected in said fluid conduit between said first and said vsecond valve means.

5. The structure as claimed in claim 1, including pressure relief valve means operative to limit the positive and negative fluid pressures developed in said conduit to predetermined maximum values.

6. The structure as claimed in claim 1, including a flow restricting valve means inserted in said iluid conduit between said' first and said second valve means.

7. The structure as claimed in claim 1, including an air reservoir connected in said fluid conduit between said first and second valve means, a vacuum relief valve and a pressure relief valve connected to said air reservoir and a ow restricting valve inserted between said air reservoir and said second valve means.

8; In an instrument testing device for testing v pressure-responsive instruments and the like, a

test fluid-pressure conduit adapted to be coninstruments .to be tested, a continuously driven pump operatively connected to said test fluidpressure conduit, means for selectively causing said pump to develop a pressure above or below atmospheric pressure in said test conduit, a reservoir connected to said conduit in the line of ow therethrough, a restricting valve for restricting the flow in either direction through said test conduit, master fluid pressure measuring means, and a connection between said measuring means and said test conduit; including a pressure conduit for measurement of pressure above atmospheric pressure, a suction conduit for measurement of pressure below atmospheric pressure and valve means operable to selectively connect either of said pressure or suction conduits to the test fluid pressure conduit and to vent the other of said conduits to the atmosphere.

9. In an instrument for testing pressure-responsive instruments and the like, a test uidpressure conduit adapted to be connected at one end thereof to pressure or vacuum instruments to be tested, a continuously driven pump operatlvely connected to said test fluid-pressure conduit. means for selectively causing said pump'to develop a pressure above or below atmospheric pressure in said test conduit, a reservoir connected to said test conduit in the line of flow therethrough, a restricting valve for restricting ow through said conduit in either direction, master fluid-pressure measuring means, and a connection between said measuring means and said test conduit; including a pressure conduit for measurement of pressure above atmospheric pressure, a suction conduit for measuring pressure below atmospheric pressure, valve means operable to selectively connect either of said pressure or suction conduits and to vent the other of said conduits to the atmosphere and means connecting said valve means with the means for selectively causing said pump to develop a iluid pressure above or below atmospheric pressure in said test Huid-pressure conduit for simultaneous operation therewith.

HARVEY NEWTON LUMM. 

